1. Field of the Invention
This invention relates generally to well completion and remedial procedures including reducing the undesirable flow of water from subterranean zones, and more particularly, to improved polymeric compositions and methods for use in well applications.
2. Description of the Prior Art
Sealing compositions have heretofore been utilized in subterranean well completion and remedial operations. For example, sealing compositions have been used in well completion operations whereby casings and liners are sealed in well bores. In performing such operations, a sealing composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a casing string or liner disposed therein. The sealing composition is permitted to gel or set in the annular space thereby forming an annular sealing mass therein. In remedial operations carried out in wells, sealing compositions are used to seal holes or cracks in casings and liners and in the sealing masses maintaining the casings and liners in well bores.
Oil and gas wells very often produce water in addition to the desired hydrocarbons. If the ratio of water produced to hydrocarbons produced by a well is relatively low, the produced water can be separated from the hydrocarbons and disposed of in a manner which does not make the operation of the well uneconomical. However, if uncontrolled large quantities of water are produced in addition to hydrocarbons by a well, the cost of pumping, handling, storing and disposing of the produced water often makes the continuing operation of the well uneconomical.
Polymeric compositions which form polymerized and crosslinked impermeable masses have been developed and used heretofore in well completion and remedial operations. For example, polymeric compositions have heretofore been used to reduce or terminate the flow of water from a subterranean zone penetrated by a well. Such compositions are introduced into a subterranean water producing zone and caused to polymerize and crosslink therein whereby a stable gel which reduces or terminates the water flow from the zone is formed therein. U.S. Pat. Nos. 3,334,689 issued Aug. 8, 1967 and 3,490,533 issued Jan. 20, 1970, both to McLaughlin, disclose polymerizable monomer solutions containing a polymerization catalyst for injection into subterranean zones. The solutions polymerize and are crosslinked in the zones to form stable gels which reduce the water permeabilities of the zones and decrease or terminate the flow of water therefrom.
U.S. Pat. Nos. 5,335,726 issued on Aug. 9, 1994 and 5,358,051 issued Oct. 25, 1994, both to Rodrigues, disclose methods of forming polymeric gels in subterranean zones to reduce or shut off the flow of water therefrom wherein a monomer is polymerized in the formation in the presence of a crosslinker by an initiator selected from certain azo compounds. Also, the use of hydroxy unsaturated carbonyl monomers is disclosed.
The aqueous solutions of monomer or monomer and crosslinker and a polymerization initiator have heretofore been pumped as low viscosity solutions into subterranean zones in which completion or remedial procedures are to be conducted. The low viscosity solutions polymerize after placement which results in the formation of sealing gels in the zones.
The polymerization of the monomer utilized is not initiated by the polymerization initiators heretofore used and/or does not proceed at an appreciable rate until oxygen-induced polymerization inhibition is overcome. That is, a polymeric solution contains dissolved oxygen which inhibits the polymerization of the monomer in the solution until all of the oxygen is consumed. The time required for the initiator to react with the oxygen present in the solution is known as the "induction period." The induction period enables placement of the polymeric solution in the zone to be sealed or plugged before polymerization of the solution prevents its flow into the zone.
While various polymerization initiators such as persulfates, peroxides and azo compounds have been utilized heretofore, azo compounds are generally preferred for the reason that they are less likely to cause premature gelation. Persulfates and peroxides are subject to premature oxidation-reduction activation when they contact certain reductants such as metal ions which are commonly encountered in well tubular goods and the like.
In performing completion or remedial operations in subterranean zones which exist at low temperatures, i.e., temperatures below about 70.degree. F., normal quantities of azo polymerization initiators do not generate radicals for reacting with oxygen at a sufficient rate to overcome the oxygen inhibition in the time required. Consequently, high concentrations of azo polymerization initiators have heretofore been utilized in the polymeric solutions utilized in low temperature applications to shorten the induction time. In some cases, the solubility limits of the polymeric composition don't allow a high enough concentration of initiator to be dissolved in the composition. In other cases, the required high initiator concentration can be dissolved, but the sealing procedure is very costly due to the high cost of the high quantity of azo initiator required.
In performing a completion or remedial operation using a polymeric composition in a subterranean zone which exists at a high temperature, i.e., a temperature above about 170.degree. F., azo polymerization initiators relatively rapidly decompose and generate free radicals which react with oxygen at a rate such that the oxygen is consumed in too short a time. That is, the oxygen in the polymeric composition is consumed too fast whereby the polymeric composition often can not be pumped into the desired subterranean zone prior to the gelation of the polymeric composition taking place.
Thus, there are needs for improved polymeric compositions and methods for performing well completion and remedial operations whereby the induction periods of the polymeric compositions can be economically shortened when the compositions are used in low temperature applications and lengthened when the compositions are used in high temperature applications.